Cohabitation agreement/How to evidence domestic abuse
I'm wanting some advice about how to go about getting a cohabitation agreement or deed of trust (I'm not sure which), as I have stupidly bought a house with my partner a few months ago (unmarried), and it's very volatile due to his alcoholism (drinking 20-30units a day with multiple hidden bottles of spirits) and he can be very verbally abusive. I put in more deposit than him (about 97k vs 67k) and as it's a big renovation project I am funding all of the initial work with 80k left over from my previous house sale. How much would this sort of thing usually cost and how long does it take to get drawn up? I feel that time is of the essence as I have reported him to the police yesterday for drink driving (I suspect he has done this multiple times recently and had dented the side of his car the other evening and arrived home stinking of alcohol, and then yesterday he got in the car after about 20 units of alcohol so I called 999 but unfortunately they didn't pull him over before he go to his destination). I have also spoken to his GP today to get it documented and they have referred me to the local domestic abuse service.
We have a 5 year mortgage and it would be a 25k fine to get out of it, so I am very loathe to sell the house as would be losing a huge amount if he also takes half what I have put in, but I also can't afford the payments by myself. On the day of completion he started shouting at me that he would be taking half of my money and has said this a few times since, but at other points said he hasn't meant this and that he would sign something, and other times said I am 'blackmailing' him by bringing the idea up. So I have no idea if he would sign something that protected my input even if I pay for it.
We have 2 young children and what has put me off ending the relationship is the idea that he could get joint custody as he is very neglectful and I don't think the children would be safe. Whereas if I stick with it at least I am there for them. He is meant to do childcare one day a week but his idea of this is to take the toddler to Wetherspoons, then arrange to work online for hours in the afternoon then just leave her in her room and hope she naps. He would never e.g. get up in the night if they needed him, and will just put monitors on silent while getting drunk e.g. one evening he had ignored our then one year old while she had clearly been vomiting repeatedly all evening and hadn't checked on her once when I was out. He doesn't put them in carseats properly and was very rough with the toddler yesterday in the bath, rubbing shampoo all over her face then pushing her over. With me he repeatedly calls me names e.g. mentalist, sociopath, c*, manipulative, controlling etc. Often won't have any sort of conversation, even asking how his day was can lead to 'you should have been in the gestapo, you're giving me gbh of the earhole', etc, or just outright blanking me. He regularly storms off sometimes not coming home all night and ignoring all calls, or falls 'asleep' at the office so doesn't come home, and embarrasses me in public, such as storming out of a restaurant the other day telling me I could pay for everything so I had to, even though it was mostly his drink. He has smashed doors and mugs etc when angry. Or does things like ask for a particular meal and when I have finished cooking it declares he isn't hungry or is ordering a takeaway instead to try and upset me. He forgot to do my stocking at Christmas despite knowing I was doing one for him and then kids, and then wrapped up some batteries and tea lights and a few other non presents and seemed to find it funny/couldn't understand why I was upset. And recently had said he would be back to look after the kids one evening so I could go to a gig, we discussed it 3 times including the night before, then he didn't turn up and eventually came back when called yelling at me and claiming we had never agreed anything and that he knew nothing about it. He has also banned me from going in the office at home telling me it is his and only his and when I disputed this he disappeared for the entire night and next morning.
What evidence should I be collecting or would stand up in court towards whether or not he gets joint custody and to show that he is abusive? I am writing down what is happening each day and taking photos of bottles I find and made a few sneaky videos of the way he speaks to me. Does anyone have experience of this sort of case and whether he is still likely to be awarded joint custody? I feel very stuck and that I have got myself into a stupid situation. In between times he can be the most charming, articulate and confident man and I'm sure would present himself well and convincingly or make out that I am lying. I often cannot believe he is the same person day to day with the rapid changes in persona.
Thanks if you've made it this far and any advice is hugely appreciated.